1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a method for network entry in a wireless communication system.
2. Discussion of the Related Art
A conventional network entry method in a wireless communication system will be described below with reference to FIGS. 1, 2 and 3. FIG. 1 is a flowchart illustrating a conventional network entry operation in a wireless communication system.
A Subscriber Station (SS) performs network entry, upon power on or when it loses communication with its serving cell or moves into a new cell. The network entry involves 10 steps.
Referring to FIG. 1, for initial access upon power-on, the SS searches for a connectable Base Station (BS) by scanning DownLink (DL) channels. Because the SS has no knowledge of a network topology or configuration at first, the SS scans the frequencies of neighbor BSs one by one.
After the SS finishes all system settings by acquiring DL and UpLink (UL) system information from a detected BS, it performs a ranging procedure with the detected BS. The SS synchronies a UL timing with the BS by contention-based ranging. For the contention-based ranging, the SS randomly selects a Code Division Multiple Access (CDMA) code and transmits the CDMA code to the BS.
Until the synchronization is completed, the BS notifies the SS of parameters to be adjusted by a Ranging Response (RNG-RSP) message. While the parameters are being adjusted, Status is set to “continue” in the RNG-RSP message. After the parameters are completely adjusted, the BS transmits an RNG-RSP message with Status set to “success” to the SS.
The SS negotiates basic capabilities with the BS. If the SS acquires synchronization completely with the BS after authentication, it registers to a broadband network and receives a service from the BS over the broadband network.
During the network entry, the SS and the BS transmit and receive Medium Access Control (MAC) messages such as Advanced Air Interface Ranging Request/Response (AAI_RNG-REQ/RSP), AAI SS Basic Capability Request/Response (AAI_SBC-REQ/RSP), AAI Privacy Key Management Request/Response (AAI_PKM-REQ/RSP), AAI Registration Request/Response (AAI_REG-REQ/RSP), etc. Conventionally, whenever the SS transmits a MAC message, it requests UL resource allocation to the BS in order to transmit the MAC message.
FIG. 2 is a diagram illustrating a signal flow for a Bandwidth Request (BR) operation of a Mobile Station (MS) in a conventional wireless communication system, and FIG. 3 is a diagram illustrating a signal flow for a BR operation of an MS in a future wireless communication system.
Referring to FIG. 2, an MS selects a code from a set of codes classified as BR codes among ranging codes and transmits the selected code to a BS in order to request a UL bandwidth in step S210. Upon successful receipt of the code from the MS, the BS allocates UL resources to the MS so that the MS may transmit a Bandwidth Request (BW-REQ) message in the allocated UL resources in step S220. In the meantime, after transmitting the code, the MS activates a timer. If the MS fails to receive a UL resource assignment from the BS until the timer expires, it retransmits the code. The timer may be set to a contention-based reservation timeout or a value T3.
In step S230, the MS transmits a BW-REQ message to the BS in the allocated UL resources. Upon receipt of the BW-REQ message from the MS, the BS allocates UL resources to the MS in step S240 and the MS transmits data in the allocated UL resources to the BS in step S250.
In the future-generation wireless communication system, a BS supports both a 5-step regular BR procedure and a 3-step quick access BR procedure. The 5-step regular BR procedure may be performed independently of the 3-step quick access BR procedure or as a fallback mode of the 3-step quick access BR procedure.
Referring to FIG. 3, in the 3-step quick access BR procedure, the MS transmits a BR indicator that is randomly selected or selected according to a predetermined rule and a quick access message to the BS in step S310. The BR indicator may be a BR sequence or a BR code, and the quick access message carries UL BR information such as a Station Identifier (STID), a request size, etc. The BS may transmit an ACKnowledgment (ACK) for the received BR indicator to the MS.
Upon successful receipt of the BR indicator and the quick access message, the BS allocates UL resources to the MS by a UL basic assignment Advanced-MAP (A-MAP) Information Element (IE) in step S340 and the MS transmits data in allocated UL resources to the BS in step S350. The MS may piggyback additional UL BR information along with the data in step S350.
In the 5-step regular BR procedure, the MS transmits a randomly selected BR indicator in step S310. Upon successful receipt of the BR indicator, the BS allocates UL resources to the MS by a CDMA allocation A-MAP IE so that the MS may transmit a BW-REQ message in the allocated UL resources in step S320. In step S330, the MS transmits a BW-REQ message in the allocated UL resources to the BS. The BS then allocates UL resources to the MS by a UL basic assignment A-MAP IE in step S340 and the MS transmits data in the allocated UL resources in step S350. The MS may piggyback additional UL BR information along with the data in step S350.
Conventionally, each time an MS is to transmit a MAC message during network entry, the MS requests UL resource allocation to a BS, for transmission of the MAC message. As a consequence, the network entry is delayed.